Chebyshev filter cutoff frequency
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Hello, I have this code corresponding to a chebyshev filter and the graph that matlab returns to me. The question is, is the cutoff frequency that of the black line (2 on the x-axis) or the green line when it intersects the blue line at 0.7?
The problem specifies that "the bands must be limited by half the power frequencies (0.707 of the maximum transfer value, or -3 dB)".
Fs = 4400;
Fn = Fs/2;
n = 3; Rp = 0.5;
Wn = [250 2000]/Fn;
[b a]=cheby1(n,Rp,Wn,'bandpass')
[h,w]=freqs(b,a)
plot(w,abs(h))
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Star Strider
am 6 Aug. 2021
We’ve been through this several times already.
For a Chebyshev Type I filter, the cutoff frequency is defined as the frequency where the passband crosses the value for the ripple amplitude. Here, it would be -0.5 dB.
If you want the cutoff frequency of this filter to be defined as the -3 dB point, define the ripple amplitude as 3 dB.
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